John Prescott

Acquired flavor acceptance and intake facilitated by monosodium glutamate in humans.

Monosodium glutamate (MSG) is known to enhance liking for the flavor of savory foods, but whether associations between flavors and effects of MSG lead to changes in subsequent liking and intake for the flavor alone is unclear. To test this, 32 volunteers evaluated and consumed a novel savory soup with no added MSG before and after four training sessions where the same soup was consumed either unchanged (Control) or with added MSG. The addition of MSG during training increased both pleasantness and savory character of the soup and resulted in a larger increase in rated pleasantness of the soup in the MSG-trained relative to control condition when the soup was re-evaluated Post-training without MSG. There was also a significant increase in voluntary soup intake Post-training after the soup had been paired with MSG but not in the Control condition, and rated hunger increased more after tasting the soup Post-training in the MSG-trained but not Control condition. These findings demonstrate that co-experience of a savory flavor and MSG can result in increased subsequent liking and intake for the flavor in the absence of MSG, and possible explanations for how MSG reinforces learning are discussed.

Inhibition of evaluative and perceptual odour-taste learning by attention to the stimulus elements

Pairing of odours and tastes in solution results in the odour taking on the tastes hedonic and perceptual properties. Theoretical accounts of such conditioning propose that the stimulus elements form a configuration with hedonic and/or perceptual properties. One implication of this account is that configural binding may be inhibited by allocation of attention to the individual elements during conditioning (analytical attention). This was tested here by training participants to attend analytically or synthetically during pairing of odours with either sucrose or water. Differential conditioning effects for sucrose- and water-paired odours were seen only in the synthetic group, with sucrose-paired odours increasing in both smelled sweetness and liking. These data support configural models as explanations for these forms of associative learning and emphasize the role of top-down processes in mediating transfer of perceptual and hedonic properties from tastes to odours.

Acquired hedonic and sensory characteristics of odours: Influence of sweet liker and propylthiouracil taster status

Repeated pairings of novel food-related odours with sweet tastes can result in enduring changes in sweetness of the odour alone, but have less consistent effects on odour liking. Variation in ability to taste propylthiouracil (PROP) might account for this, since PROP supertasters (ST) have been reported both to experience stronger sweetness intensity and to be more likely to dislike sweetness than do PROP nontasters (NT). Alternatively, individual differences in liking for sweetness may transfer to sweet-paired odours independently of PROP sensitivity. To explore this, evaluations of sucrose, saccharin, and PROP solutions were used to classify 92 volunteers as either sweet likers or dislikers and as PROP ST, NT, or medium tasters (MT). Changes in pleasantness of odours that had been paired with the taste of saccharin increased in sweet likers but decreased in dislikers. Odour sweetness increased regardless of PROP taster or sweet liker status. PROP ST rated saccharin as more bitter than did other taster groups and also showed greater increases in acquired bitterness of the saccharin-paired odour. Overall, these data suggest that individual differences in evaluation of saccharin reliably predict subsequent changes in evaluation of saccharin-paired odours, with hedonic changes corresponding with liking for sweet tastes and sensory changes reflecting differences in sensory quality between PROP taster groups.

The effects of a reduced sodium, high potassium salt substitute on food taste and acceptability in rural northern China

A potassium chloride-containing salt substitute lowers blood pressure levels, but its overall acceptability has been of concern due to its potential adverse effects on food taste. In a large-scale, blinded randomised trial evaluating the comparative effects of a salt substitute (65 % sodium chloride, 25 % potassium chloride and 10 % magnesium sulphate) and a normal salt (100 % sodium chloride) on blood pressure, we collected data on the saltiness, flavour and overall acceptability of food. We performed this at baseline, 1, 6 and 12 months post-randomisation using 100 mm visual analogue scales for assessments of both home-cooked foods and a standard salty soup. The mean age of the 608 participants from rural northern China was 60 years and 56 % of them were females. In the primary analyses, the changes in the saltiness, flavour and overall acceptability of both home-cooked foods and a standard salty soup were not different between the randomised groups (all P>0.08). In the secondary analyses, weighting each of the data points according to the lengths of the respective follow-up intervals, the flavour of both home-cooked foods (mean difference = - 1.8 mm, P = 0.045) and a standard salty soup (mean difference = - 1.9 mm, P = 0.03) was slightly weaker in the salt substitute group. We conclude that salt substitution is both an effective and an acceptable means of blood pressure control. Possible small differences in flavour did not importantly deter the use of the salt substitute in this study group, although the acceptability of the salt substitute by a more general population group would need to be confirmed.

Rating a new hedonic scale: a commentary on "derivation and evaluation of a labeled hedonic scale" by Lim, Wood and Green.

To the extent that our experiences of tastes and odors haveunderlyingdimensions, onecanmountastrongcase thattheexpression of those dimensions is via hedonics (Scott andMark1987;Khanetal.2007).Thehedonicdimensioniscru-cialin defining responses in the chemical senses in awaythatis not true for other senses, in that all chemosensory stimuliare intrinsically valenced, either at birth (e.g., in the case ofsweetness and bitterness) or as a result of our subsequent ex-perienceswiththem(arguablythecaseforallodorqualities).Traditional psychophysics, developed primarily for studiesin vision, audition or touch, asks questions about stimulusintensity, but this may be of less importance for taste orsmell, which derive much of their meaning from theirhedonic properties. Moreover, certainly in the case of tastequalities, our hedonic responses may provide crucial cluesregarding the adaptive significance of those qualities. Assuch, the overall paucity of attempts to ‘‘fine tune’’ our psy-chophysical methods in relation to chemosensory hedonicsis all the more puzzling.Even in the tortoise world of psychophysics, the develop-mentofhedonicmeasurementhasbeenstartlinglyslow.Thismay be because much of the interest in psychophysical mea-surement has been centered on addressing the question ofhow best to directly access perceptual processes, that is, tocharacterize sensory systems in psychological terms, whichcouldthenbeusefullylinkedtounderlyingphysiologicalpro-cesses. The importance of the development of the LabeledMagnitude Scale (LMS), first published in 1993 (Green et al.1993), and later modified as the general (g)LMS (Bartoshuket al. 2002), lies in the attempt to provide a means of scalingconsistent with S.S. Steven’s psychophysical model, whichspecified a relationship between physical stimulus magni-tude and sensation in ratio terms. Magnitude estimation(ME), derived from the same theoretical base, enjoyed a pe-riod of application that has waned in recent decades. It hasbeen suggested that the primary reasons for ME falling outof favor was both that people do not themselves consis-tently use numbers in a ratio fashion and also that the mea-surement process itself was unwieldy because of the priortraining that was deemed necessary. Thus, the introductionof the LMS was timely, quickly being adopted by manypsychophysical researchers, especially those hoping fora measurement free of the context of the stimuli under mea-surement (Bartoshuk 2000).Accessing ‘‘secondary states,’’ including the hedonic eval-uationofsensorystimuli,hasbeenregardedaslessimportantbecauseithasbeenfeltthatthestimulus-affectiverelationshipis less direct (although there is evidence that affective statesmight occur in the absence of perceptual awareness—seeKunst-Wilson and Zajonc 1980), has less to tell us aboutperception per se, and is further from being ‘‘objective,’’ inthataffectivestatesclearlyshowconsiderableindividualvar-iability(often,oforiginunknown).Ironically,todate,oneofthemostcommon applicationsofthe gLMShasbeeninthestudyofindividualdifferencesinperception,particularlyinrelationtooralirritationand6-n-propylthiouracilbitterness(Bartoshuk 2000; Prescott et al. 2001; Green and Hayes2003). One of the benefits of the gLMS is that, via the useofasupposed(andperhaps,inpractice,actual)frameofref-erence external to the stimuli themselves, generated by thetop-end label ‘‘Strongest Imaginable Sensation of AnyKind,’’wecanminimizethegenerallyuninterestingvariabil-ityassociatedwithscaleusageandmaximizethequiteinter-esting variability associated with individual perceptual orphysiological differences. Affective states and responsesare, of course, expected to show considerable individual

Olfactory conditioning reinforced by saccharin in humans: Influence of prop taster and sweet liker status

Repeated retronasal exposure to novel food odours with sweet and bitter tastes can lead to subsequent changes in orthonasal liking and sensory experience of the taste-paired odours. PROP tasters have been reported to rate low concentrations of saccharin as more bitter and less sweet than do PROP non-tasters. We therefore predicted that acquired liking for, and sweetness and bitterness of, odours conditioned by association with saccharin would vary depending on PROP taster status. 87 volunteers evaluated two novel odours before and after co-experience of one odour with 4 mM/l saccharin and the second with water. PROP taster status was assessed from the intensity of 3.2 mM PROP relative to 1.0 M NaCl, and sweet-liker status from liking ratings for 0.21 and 0.83 M/l sucrose and 0.0004 M/l and 0.0010 M/l saccharin. Liking for the saccharin-paired odour increased in sweet likers but decreased in sweet-dislikers. Overall liking change also varied with PROP taster status, with both odours rated less pleasant post-training in the super-taster and taster but not non-taster groups. The saccharin-paired odour was rated sweeter post-training, regardless of PROP taster or sweet-liker status. PROP super-tasters rated the saccharin-paired odour as more bitter post-training, in-line with enhanced bitterness of saccharin in this group. These data confirm that sensory and hedonic changes operate independently olfactory conditioning, and are influenced by individual differences in sensitivity to bitter and sweet stimuli.